This invention is generally directed to a novel method of punching a composite plate.
One prior art method of punching a hole in a composite plate, which is formed of first and second skins with a core sandwiched therebetween, was performed by punching a hole through the plate with a single punch by using a punching apparatus. Due to the spring back qualities of the core material, the core material entered into the hole formed by the punch after the punch was removed from its engagement with the plate. Therefore, the hole created by the punch was not clear and a rivet could not be placed therethrough without first completely clearing the hole by using separate, special tools.
The special tools are used to drill out or remove the excess core material within the hole. These tools are expensive and the process of removing the excess core material is labor intensive.
Another prior art method which is disclosed in this inventor's U.S. Pat. No. 5,774,972, and which is commonly owned by the Assignee herein, uses a novel double punching method to punch the composite plate. This method eliminates the need for special tools to drill out or remove the excess core material within the hole. A problem has been found with this method in that, at times, when the punch is driven completely through the first overlaying skins, the core and the second skin, after breaking the first skins and driving them through the core, the first skins sometimes slipped to the side of the punch, causing the resulting hole to be improperly aligned.
The present invention resolves the problems found in the prior art. The present invention provides a novel method for punching a composite plate which eliminates the step of drilling out or removing excess core material within the hole by using a separate tool and eliminates improper alignment of the resulting hole. In addition, the method of the present invention presents several other advantages and features including the provision of a novel joint structure which will become apparent upon a reading of the attached specification.